Paint and other liquid mixtures can be stored in a container having a cylindrical side wall, a circular head wall, and a circular bottom wall. Such a container is commonly called a “drum” and the walls are formed from sheet metal, such as steel. A typical industrial size for such a container is a fifty-five gallon drum. The liquid mixtures (e.g., paint) often contain materials which tend to settle to the bottom by gravity, whereby an agitator is incorporated into the container design so that the liquid can be mixed prior to its use.
A popular agitator design includes a shaft and an impeller attached to the shaft. The bottom end of the shaft is supported rotatably by the drum's bottom wall, and the upper end of the shaft is adapted for coupling to a motor drive shaft. To operate the agitator, a motor is mounted on the drum's head wall and the agitator shaft is coupled to the motor's drive shaft. Upon activation of the motor, rotational motion is transferred to the agitator shaft, causing the impeller to turn and thereby agitating the liquid. The shaft and impeller can be designed to be removable from the drum between agitation cycles. However, of particular relevance in the present case is an agitator design wherein the shaft and impeller remain in the drum, and only the motor is removed between agitation cycles.
The drum's head is designed to afford convenient mounting of the motor and to allow access to the agitator shaft for coupling thereto. To this end, the head wall typically includes a central opening defined by an annular flange, which is attached to the surrounding circular sheet metal edge. The flange includes interior threads (i.e., threads on its radially inward surface), which engage with exterior threads on a mounting component of the motor. Upon mounting of the motor, its drive (or coupling) shaft extends through the central opening and is coupled to the agitator shaft so that rotational motion may be transferred thereto.
Accordingly, the diameter of the drum's threaded flange must be compatible with the diameter of the motor's threaded mounting component. For example, in the paint industry, many motors are designed for mounting within an 1½ inch threaded flange. If a drum has a different sized flange (e.g., 2 inches), the motors mountable on an 1½ inch flange cannot be used, whereby such a drum probably would not be purchased. In addition to convenient motor-mounting, a drum design also must incorporate means for maintenance of the agitator shaft in an upright position so that, when the motor is coupled to the drum, the agitator shaft will be positioned for coupling to the motor shaft. This can be accomplished by installing (e.g., welding) a metal bracket to the interior surface of the drum's head wall, which will hold the shaft upright within the drum.